A disadvantage of conventional cassettes is that the user can only estimate the position of the magnetic tape in relation to one of its ends, when a cassette is reintroduced by the user in a tape deck. Conventional cassettes are provided with transparent windows permitting direct observation of the thickness of the winding of the magnetic tape on one or the other of the reels; however this method of estimating position is completely lacking in precision because of the extreme thinness of the tape.
It has also been proposed, in order to improve the precision of mechanisms for indicating tape position to fit mechanical movement indicators in or on the cassettes, but their complexity and bulkiness is such that practically no cassette can contain them. Moreover, as their precision remains unacceptable and their selling price is very high, while these mechanical indicators have been proposed in prior art patents they have found little if any commercial use.